The inventive concepts described herein generally relate to non-volatile memory devices, and more particularly, the inventive concepts relate to non-volatile memory devices having memory cells arranged in a direction perpendicular to a substrate, and to operating methods of a non-volatile memory devices having memory cells arranged in a direction perpendicular to a substrate.
Memory devices are generally categorized as either volatile or non-volatile. A volatile memory device is characterized by the loss of stored data at a power-off state, whereas in contrast a non-volatile memory device is characterized by the retention of stored data at a power-off state. Examples of non-volatile memory include read only memory (ROM), electrically erasable programmable ROM (EEPROM), and the like.
Developed from EEPROM technology, a flash memory device is a type of non-volatile memory in which erase operations are carried out in units of memory blocks, and program operations are carried out in units of bits.
Flash memory is programmed by controlling a threshold voltage state of a memory cell. However, the programmed threshold voltage of a memory cell can vary as the result a variety of causes, such as floating gate coupling, charge loss over time, and so on. Any such variation in the programmed threshold voltage of a memory cell can adversely impact the reliability of a read operation.
Conventionally, flash memory cells have been formed in a two-dimensional array lying parallel to an underlying substrate. Recently, however, three-dimensional flash memory configurations have been developed which include memory cells arranged in a direction perpendicular to an underlying substrate.